Substrate for liquid crystal display and method of fabricating the same

ABSTRACT

A color filter substrate for a liquid crystal display includes a transparent substrate, and color filters formed on the substrate each with a groove. A transparent conductive layer is deposited onto the color filters to form a common electrode. A chrome layer and a chrome oxide layer are sequentially deposited onto the common electrode to form a black matrix layer. An organic film is formed on the black matrix layer. The organic film suffers ashing such that only the portion of the organic film placed over the groove is left over, and other portions are all removed while exposing the black matrix layer. The exposed portion of the black matrix layer is removed through etching. In this way, the color filter substrate is completed in a simple manner.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.10/894,026 filed on Jul. 20, 2004, which is a divisional of U.S. patentapplication Ser. No. 10/040,478 filed on Jan. 9, 2002, which claimspriority to Korean Patent Application Ser. No. 2001-1138, filed on Jan.9, 2001, the disclosures of which are incorporated by reference herein.

BACKGROUND OF THE INVENTION

(a) Field of the Invention

The present invention relates to a liquid crystal display and, moreparticularly to a color filter substrate for a liquid crystal display.

(b) Description of the Related Art

Generally, liquid crystal displays have a structure where a liquidcrystal is sandwiched between two substrates, and an electric field isapplied to the liquid crystal to control light transmission. Among thesubstrates, the bottom substrate is provided with thin film transistorsand pixel electrodes, and usually called the “thin film transistor arraysubstrate.” The top substrate is provided with a common electrode andcolor filters, and usually called the “color filter substrate.”

In order to fabricate such a liquid crystal display at a lower costwithin reduced time period, it is necessary to simplify thephotolithography process that involves complicated processing steps.

FIGS. 1A through 1D sequentially illustrate the steps of fabricating acolor filter substrate for a liquid crystal display according to a priorart.

As shown in FIG. 1A, a chrome oxide layer 21 and a chrome layer 22 aresequentially deposited onto a transparent glass substrate 10, andpatterned through photolithography to thereby form a black matrix 20.

As shown in FIG. 1B, color filters 30 of red, green and blue colors areformed on the substrate 10 with the black matrix 20 though performingphotography three times. In the photography process, a layer based on aphotosensitive material containing pigment is deposited onto thesubstrate 10, exposed to light, and developed.

As shown in FIG. 1C, a common electrode 40 is formed on the colorfilters 30 with a transparent conductive material such as indium tinoxide (ITO).

In the case of twisted nematic (TN) mode liquid crystal displays, thecolor filter substrate is completed through the above processing steps.That is, the color filter substrate is fabricated through performingphotolithography one time, and photography three times.

However, in case opening portions are formed at the common electrode andthe pixel electrodes to obtain wide viewing angle characteristic with apatterned vertically aligned (PVA) mode, an additional process ofphotolithography should be introduced. That is, as shown in FIG. 1D,opening portions 41 are formed at the common electrode 40 throughphotolithography.

Furthermore, when the opening portions 41 are formed at the commonelectrode 40, the color filters 30 suffer damages during the etchingprocess while being exposed through the opening portions 41, and thisdeteriorates the property of the liquid crystal.

In order to solve such problems, it has been suggested that protrusionsbased on an organic material should be formed at the common electrode 40instead of the opening portions 41, or opening portions and protrusionsshould be formed only at the pixel electrodes without patterning thecommon electrode 40. However, such techniques yet involve complicatedprocessing steps and does not provide sufficient wide viewing angle.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method offabricating a color filter substrate for a liquid crystal display whichinvolves simplified processing steps.

It is another object of the present invention to provide a liquidcrystal display which bears improved wide viewing angle characteristic.

These and other objects may be achieved by a color filter substrate fora liquid crystal display with the following features.

According to one aspect of the present invention, the color filtersubstrate includes a transparent substrate, and color filters formed onthe substrate each with a groove. A first transparent conductive layercovers the color filters, and a black matrix is formed on the firsttransparent conductive layer within the groove of each color filter.

The groove of each color filter may be filled with an organic film or aphotosensitive film. The photosensitive film is preferably covered witha second transparent conductive layer. It is preferable that the blackmatrix is formed with a double-layered structure where a chrome layerand a chrome oxide layer are present. Alternatively the black matrix maybe formed with an organic material. The black matrix has first portionsformed at the area between the neighboring color filters, and secondportions formed at the area within each color filter while partitioningthe color filter into a plurality of domains.

According to another aspect of the present invention, the color filterhas a transparent substrate, and color filters formed on the substrateeach with a groove. A black matrix is placed within the groove of eachcolor filter, and a transparent conductive layer is formed on the blackmatrix. The groove of each color filter may be filled with an organicmaterial. In a method of fabricating the color filter substrate, colorfilters are formed on a transparent substrate such that each colorfilter has a groove. A first transparent conductive layer is formed onthe color filters. A black matrix layer is deposited onto the firsttransparent conductive layer. A gap filler is formed on the black matrixlayer such that the gap filler fills the groove of each color filter.The exposed portion of the black matrix layer is removed throughetching.

The gap filler may be formed either through coating an organic film ontothe black matrix layer, and ashing the organic film, or through coatinga photosensitive film onto the black matrix layer, exposing thephotosensitive film to light, and developing the light-exposed film. Itis preferable that the black matrix layer should be formed throughsequentially depositing a chrome layer and a chrome oxide layer onto thefirst transparent conductive layer. Furthermore, a second transparentconductive layer may be formed on the gap filler.

In another method of fabricating the color filter substrate, colorfilters are formed on a transparent substrate such that each colorfilter has a groove. A first transparent conductive layer is formed onthe color filters. A black matrix is formed on the first transparentconductive layer such that the black matrix fills the groove of eachcolor filter.

A second transparent conductive layer may be formed on the black matrix.

In still another method of fabricating the color filter substrate, colorfilters are formed on a transparent substrate such that each colorfilter has a groove. A black matrix layer is deposited onto the colorfilters. A gap filler is formed on the black matrix layer such that thegap filler fills the groove of each color filter. The exposed portion ofthe black matrix layer is removed through etching. A transparentconductive layer is formed on the gap filler.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention, and many of the attendantadvantages thereof, will be readily apparent as the same becomes betterunderstood by reference to the following detailed description whenconsidered in conjunction with the accompanying drawings in which likereference symbols indicate the same or the similar components.

FIGS. 1A, 1B 1C and 1D sequentially illustrate the steps of fabricatinga color filter substrate for a liquid crystal display according to aprior art.

FIGS. 2A, 2B, 2C, 2D, 2E and 2F sequentially illustrate the steps offabricating a color filter substrate for a liquid crystal displayaccording to a first preferred embodiment of the present invention.

FIGS, 3A, 3B, 3C, 3D and 3E sequentially illustrate the steps offabricating a color filter substrate for a liquid crystal displayaccording to a second preferred embodiment of the present invention.

FIGS. 4A, 4B, 4C, 4D, 4E and 4F sequentially illustrate the steps offabricating a color filter substrate for a liquid crystal displayaccording to a third preferred embodiment of the present invention.

FIGS. 5A, 5B, 5C, 5D, 5E and 5F sequentially illustrate the steps offabricating a color filter substrate for a liquid crystal displayaccording to a fourth preferred embodiment of the present invention.

FIGS. 6A and 6B are sectional views illustrating the orientation stateof liquid crystal molecules under the application of voltages to acommon electrode and a pixel electrode for the liquid crystal displaysaccording to the preferred embodiments of the present invention;

FIG. 7A is a schematic view of a black matrix of a color filtersubstrate for a liquid crystal display according to a fifth preferredembodiment of the present invention;

FIG. 7B is a schematic view of a thin film transistor array substratefor the liquid crystal display according to the fifth preferredembodiment of the present invention;

FIG. 7C is a schematic view of the liquid crystal display where thecolor filter substrate shown in FIG. 7A and the thin film transistorarray substrate shown in FIG. 7B are assembled with each other;

FIG. 8A is a schematic view of a black matrix of a color filtersubstrate for a liquid crystal display according to a sixth preferredembodiment of the present invention;

FIG. 8B is a schematic view of a thin film transistor array substratefor the liquid crystal display according to the sixth preferredembodiment of the present invention; and

FIG. 8C is a schematic view of the liquid crystal display where thecolor filter substrate shown in FIG. 8A and the thin film transistorarray substrate shown in FIG. 8B are assembled with each other.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of this invention will be explained with referenceto the accompanying drawings.

FIGS. 2A through 2F illustrate the steps of fabricating color filtersubstrate for a liquid crystal display according to a first preferredembodiment of the present invention.

As shown in FIG. 2A, color filters 30 of red, green and blue colors areformed in a transparent insulating substrate 10 through performingphotography three times. That is, as related to each color, a layerbased on a photosensitive material containing pigment is deposited ontothe substrate 10, exposed to light through a mask, and developed. Agroove is formed at a predetermined portion in order to make a domainpartitioning pattern) of each color filter 30, and at the area betweenthe neighboring color filters 30. It is preferable that the grooveshould bear a depth so large as to expose the underlying transparentsubstrate 10. The width of the groove is preferably in the range of 5-15.mu.m, more preferably about 8 .mu.m.

As shown in FIG. 2B, a common electrode 40 is formed on the colorfilters 30 with a transparent conductive material such as indium tinoxide (ITO) and indium zinc oxide (IZO).

As shown in FIG. 2C, a chrome oxide layer 21, and a chrome layer 22 aresequentially deposited onto the common electrode 40 to thereby form ablack matrix layer 20.

As shown in FIG. 2D, an organic film 50 is coated onto the black matrixlayer 20. The organic film 50 may be formed with an acryl-basedmaterial, or a BCB-based material. The BCB-based material is preferredfor the organic film 50 in view of wide viewing angle characteristic.The organic film 50 preferably has a thin thickness of 0.5-3.5 .mu.mwhile filling the groove.

As shown in FIG. 2E, the organic film 50 suffers ashing through dryetching such that only the portion thereof at the groove is left overand other portions are all removed while exposing the underlying blackmatrix layer 20. The dry etching usually bears an etching ratio of 150.ANG. per second. Thus, assuming that the organic film 50 has athickness of about 1.5 .mu.m, one hundred seconds are consumed for theetching. At this time, over-etching of 5-50% is preferably made toobtain sufficient margin.

Finally, as shown in FIG. 2F, the exposed portion of the black matrixlayer 20 is removed through etching. At this time, the portion of theblack matrix layer 20 at the groove is left over while being protectedby the organic film 50.

Consequently, a color filter substrate is completed. The black matrixprevents leakage of light. The groove as well as the organic filmfilling the groove controls the inclining directions of the liquidcrystal molecules.

In the above process, only photography is made three times withoutintroducing photolithography. Therefore, compared to the conventionalprocess of fabricating a TN mode color filter substrate, the process ofthe present invention eliminated the photolithography step. Furthermore,compared to the conventional process of fabricating a PVA mode colorfilter substrate, the present process eliminated two steps ofphotography. In this way, the steps of processing the color filtersubstrate can be simplified. Furthermore, forming the black matrixthrough self alignment can prevent decrease in the opening ratio due tothe misalignment of the mask.

FIGS. 3A through 3E illustrates the steps of fabricating a color filtersubstrate for a liquid crystal display according a second preferredembodiment of the present invention. In this preferred embodiment, theblack matrix is formed with an organic material.

As shown in FIG. 3A, color filters 310 of red, green and blue colors areformed on a transparent insulating substrate 10 through performingphotography three times. That is, as related to each color, a layerbased on a photosensitive material containing pigment is deposited ontothe substrate 10, exposed to light through a mask, and developed. Agroove is formed at a predetermined portion in order to make a domainpartitioning pattern) of each color filter 30, and at the area betweenthe neighboring color filters 30. It is preferable that the groove bedeep enough to expose the underlying transparent substrate 10.

As shown in FIG. 3B, a first common electrode 43 is formed on the colorfilters 30 with a transparent conductive material such as indium tinoxide (ITO) and indium zinc oxide (IZO).

As shown in FIG. 3C, an organic black matrix 60 is formed on the firstcommon electrode 43.

As shown in FIG. 3D, the organic black matrix 60 suffers ashing throughdry etching such that only the portion thereof at the groove is leftover while filling the groove, and other portions are all removed.

In this way, a color filter substrate is completed. However, when theorganic black matrix 60 contacts the liquid crystal, the liquid crystalmaterial may be contaminated due to pigment, and this causes occurrenceof after-image. In order to solve such a problem, as shown in FIG. 3E, asecond common electrode 42 may be formed on the first common electrode43 with a transparent conductive material to cover the organic blackmatrix 60.

FIGS. 4A through 4F illustrate the steps of fabricating a color filtersubstrate for a liquid crystal display according to a third preferredembodiment of the present invention.

As shown in FIG. 4A, color filters 30 of red, green and blue colors areformed on a transparent insulating substrate 10 through performingphotography three times. A groove is formed at a predetermined portion(in order to make a domain partitioning pattern) of each color filter30, and at the area between the neighboring color filters 30. It ispreferable that the groove should be deep enough to expose theunderlying transparent substrate 10. The width of the groove ispreferably in the range of 5-15 .mu.m, more preferably about 8 .mu.m.

As shown in FIG. 4B, a common electrode 40 is formed on the colorfilters 30 with a transparent conductive material such as indium tinoxide (ITO) and indium zinc oxide (IZO).

As shown in FIG. 4C, a chrome oxide layer 21, and a chrome layer 22 aresequentially deposited onto the common electrode 40 to thereby form ablack matrix layer 20.

As shown in FIG. 4D, a photosensitive film 70 is formed on the blackmatrix layer 20 with a photosensitive material, and exposed to lightthrough a mask 1 with a light interception pattern 2. It is preferablethat the photosensitive film 70 should bear a thin thickness of 0.5-3.5.mu.m while filling the groove. The mask may be structured such thateither the portion thereof placed over the groove intercepts light whiletransmitting the light at other portions (in the case of a negativephotoresist film), or the portion thereof placed over the groovetransmits light while intercepting the light at other portions (in thecase of a positive photoresist film). The mask may be provided with aslit pattern, or a semitransparent film. That is, the portion of themask with the slit pattern or the semitransparent film is placed overthe groove while reducing the amount of light illumination thereto suchthat the remaining photosensitive film 70 thorough the developingprocess only fills the groove. Alternatively, the time period of lightexposing may be varied to control the thickness of the remainingphotosensitive film 70 without using a mask.

As shown in FIG. 4E, the photosensitive film 70 is developed so thatonly the portion thereof placed over the groove is left over, and otherportions are all removed while exposing the underlying black matrixlayer 20.

Finally, as shown in FIG. 4F, the exposed portion of the black matrixlayer 20 is removed through etching. The black matrix layer 20 formed atthe groove is not etched while being protected by the photosensitivefilm 70.

In this process, only photography is made three times withoutintroducing photolithography.

FIGS. 5A through 5F illustrate the steps of fabricating a color filtersubstrate for a liquid crystal display according to a fourth preferredembodiment of the present invention.

As shown in FIG. 5A, color filters 30 of red, green and blue are formedon a transparent insulating substrate 10 through performing photographythree times. A groove is formed at a predetermined portion (in order tomake a domain partitioning pattern) of each color filter 30, and at thearea between the neighboring color filters 10. It is preferable that thegroove should be deep enough to expose the underlying transparentsubstrate 10. The width of the groove is preferably in the range 5-15.mu.m, more preferably about 8 .mu.m.

As shown in FIG. 5B, a chrome oxide layer 21, and a chrome layer 22 aresequentially deposited onto the color filters 30 to form a black matrixlayer 20.

As shown in FIG. 5C, an organic film 50 is coated onto the black matrixlayer 20. The organic film 50 may be formed with an acryl-basedmaterial, or a BCB-based material. The BCB-based material is preferredfor the organic film 50 in view of wide viewing angle characteristic.The organic film 50 preferably has a thin thickness of 0.5-3.5 .mu.mwhile filling the groove.

As shown in FIG. 5D, the organic film 50 suffers ashing through dryetching, leaving only the portion placed at the groove. And otherportions are all removed while exposing the underlying black matrixlayer 20. At this time, over-etching of 5-50% is preferably made toobtain sufficient margin.

As shown in FIG, 5E, the exposed portion of the black matrix layer 20 isremoved through etching. At this time, the portion of the black matrixlayer 20 at the groove is left over while being protected by the organicfilm 50.

Finally, as shown in FIG. 5F, a common electrode 40 is formed on thecolor filters 30 and the organic film 50 with a transparent conductivematerial such as indium tin oxide (ITO) and indium zinc oxide (IZO).

Consequently, a color filter substrate is completed. In such a colorfilter substrate, as different from the color filter substrate relatedto the previous preferred embodiments, the organic film 50 only fillsthe groove, but does not control the inclining directions of the liquidcrystal molecules.

Alternatively, an organic black matrix may be used instead of thedouble-layered black matrix 20 made of the chrome layer and the chromeoxide layer. In this case, the color filter substrate is fabricatedthrough the steps of color filter formation, organic black matrixcoating, organic black matrix ashing, and common electrode formation.

In the above process, only photography is made three times withoutintroducing photolithography. Therefore, compared to the conventionalprocess of fabricating a TN mode color filter substrate, such a processof the present invention eliminates one step of photolithography.

FIGS. 6A and 6B illustrate the orientation of liquid crystal moleculesunder the application of voltages to a common electrode and a pixelelectrode in the liquid crystal displays according to the preferredembodiments of the present invention at the initial stage of voltageapplication and at the 20 msec later stage thereof, respectively.

As shown in FIGS. 6A and 6B, equipotential lines are bent due to thegroove as well as the organic film or the photosensitive film fillingthe groove, and electric fields proceeding perpendicular to theequipotential lines are also bent. For this reason, the incliningdirections of the liquid crystal molecules are made toward predetermineddestinations. That is, the liquid crystal molecules at either side ofthe groove are inclined in the directions opposite to each other. Thiseffect is the same as that related to the opening portion in the PVAmode liquid crystal display.

FIG. 7A is a schematic view of a black matrix of a color filtersubstrate for a liquid crystal display according to a fifth preferredembodiment of the present invention.

FIG. 7A illustrates a pattern of a black matrix 20 corresponding to twopixel electrodes. The black matrix 20 has first portions 23 with a largewidth that divide the neighboring pixel regions, and second portions 24and 25 with a small width that partition one pixel region into pluralnumbers of micro-regions. The second portions of the black matrix 20 areclassified into horizontal portions 24 and vertical portions 25. Such ablack matrix 20 partitions one pixel region into four micro-regions.

FIG. 7B is a schematic view of a pixel electrode of a thin filmtransistor array substrate for the liquid crystal display according tothe fifth preferred embodiment of the present invention.

The pixel electrode 100 has two vertical opening portions 101, and twohorizontal opening portions 102.

FIG. 7C illustrates the state of assembling the color filter substrateshown in FIG. 7A and the thin film transistor array substrate shown inFIG. 7B with each other.

The opening portions 101 and 102 of the pixel electrode 100 are arrangedbetween the portions of the black matrix 20. One pixel region ispartitioned into eight micro-regions by way of the opening portions 101and 102 of the pixel electrode 100 and the black matrix 20. The eightmicro-regions proceed longitudinally in the horizontal and verticaldirections four by four. In the four vertical regions, the liquidcrystal molecules at the two regions are inclined toward east, and thoseat the two regions are inclined toward west. In the four horizontalregions, the liquid crystal molecules at the two regions are inclinedtoward south, and those at the two regions are inclined toward north. Inthis way, the liquid crystal molecules are uniformly inclined in fourdirections so that good picture images can be produced in any viewingdirection.

FIG. 8A is a schematic view of a black matrix of a color filtersubstrate for a liquid crystal display according to a sixth preferredembodiment of the present invention.

The black matrix 20 has first portions 23 with a large width that dividethe neighboring pixel regions, and a second portion 25 with a smallwidth that partition one pixel region into a number of micro-regions.Such a black matrix 20 partitions one pixel region into threemicro-regions. The two micro-regions partitioned by the second portion25 have the same horizontal width, but the remaining micro-region has arelatively narrow horizontal width.

FIG. 8B is a schematic view of a pixel electrode of a thin filmtransistor array substrate for the liquid crystal display according tothe sixth preferred embodiment of the present invention.

The pixel electrode 100 bears a first region with a small width, and asecond region with a large width. A first opening portion 101 islongitudinally extended at the first region of the pixel electrode 100in the vertical direction, and two second opening portions 102 arelongitudinally extended at the second region of the pixel electrode 100in the horizontal direction. The first region of the pixel electrode 100is bisected by way of the first opening portion 101 left and right, andthe second region of the pixel electrode 100 is trisected by way of thesecond opening portions 102 up and down. Among the trisectedmicro-regions, the width of the center micro-region is two times aslarge as the two side micro-regions.

FIG. 8C illustrates the state of assembling the color filter substrateshown in FIG. 8A and the thin film transistor array substrate shown inFIG. 8B with each other.

One pixel region is partitioned into six micro-regions by way of theopening portions 101 and 102 of the pixel electrode 100 and the blackmatrix 20. The effect pursuant to the partitioning of the pixel regionare the same as described with reference to FIGS. 7A, 7B and 7C. Thatis, wide viewing angle characteristic can be obtained in an effectivemanner.

As described above, in the inventive liquid crystal display, the colorfilter substrate can be fabricated in a simplified manner. Furthermore,as the black matrix is formed by way of self alignment, decrease in theopening ratio due to the misalignment of the mask during the blackmatrix formation process can be prevented.

While the present invention has been described in detail with referenceto the preferred embodiments, those skilled in the art will appreciatethat various modifications and substitutions can be made thereto withoutdeparting from the spirit and scope of the present invention as setforth in the appended claims.

1. A method of fabricating a liquid crystal display, comprising stepsof: forming a color filter on a transparent substrate; forming a grooveon the color filter; forming a first transparent conductive layer on thecolor filters; depositing a black matrix layer onto the firsttransparent conductive layer; forming a gap filler on the black matrixlayer to fill the groove of each color filter, and removing the exposedportion of the black matrix layer through etching.
 2. The method ofclaim 1, wherein the step of forming the gap filler comprises steps of:coating an organic film onto the black matrix layer; and ashing theorganic film.
 3. The method of claim 1, wherein the step of forming thegap filler comprises steps of: coating a photosensitive film onto theblack matrix layer; exposing the photosensitive film to light; anddeveloping the film.
 4. The method of claim 1, wherein the step ofdepositing the black matrix layer comprises steps of: depositing achrome layer on the first transparent conductive layer; and depositing achrome oxide layer on the chrome layer.
 5. The method of claim 1,further comprising a step of forming a second transparent conductivelayer to cover the gap filler.
 6. A method of fabricating a liquidcrystal display, comprising steps of: forming a color filter on atransparent substrate; forming a groove on the color filter, forming afirst transparent conductive layer on the color filter; and forming ablack matrix on the first transparent conductive layer to fill thegroove.
 7. The method of claim 6, further comprising a step of forming asecond transparent conductive layer on the black matrix.
 8. A method offabricating a liquid crystal display, comprising the steps of: forming acolor filter on a transparent substrate; forming a groove on the colorfilter depositing a black matrix layer onto the color filter; forming agap filler on the black matrix layer to fill the groove; etching toremove an exposed portion of the black matrix layer; and forming atransparent conductive layer on the gap filler.